How Much Paint Do I Need for a Room? UK Calculation Guide

You can estimate room paint by measuring wall area, subtracting openings, and dividing the total area to be covered by the paint tin’s coverage figure.

Start with the wall area

For a rectangular room, add the length and width, double the result, then multiply by wall height. This estimates the area of all four walls: 2 × (length + width) × height.

Subtract the combined area of doors and windows you will not paint. An approximate opening area is enough for an early shopping estimate, though measuring it gives a better result.

Allow for coats and coverage

Paint tins normally state an approximate coverage rate in square metres per litre. Multiply the wall area by the number of coats, then divide by the coverage rate. Coverage varies with the product, wall texture, porosity and application method, so use the figure printed on your chosen tin.

Worked example: a 4 m by 3 m room

Assume a 2.4 m wall height, a total of 4 m² of doors and windows, two coats and 10 m² of coverage per litre:

1. Four-wall area: 2 × (4 + 3) × 2.4 = 33.6 m².
2. After openings: 33.6 − 4 = 29.6 m².
3. Two coats: 29.6 × 2 = 59.2 m² to cover.
4. At 10 m²/L: 59.2 ÷ 10 = 5.92 litres.
5. With 10% extra: 5.92 × 1.10 = 6.51 litres approximately.

Choose a practical combination of tin sizes based on your product and expected touch-ups. This is a wall-only estimate; ceilings, woodwork and primer need separate allowances.

What changes the amount of paint?

• New plaster or highly absorbent surfaces may need preparation or a suitable first coat.
• A strong colour change can require additional coats.
• Textured walls and some application methods use more paint.
• Different products may recommend different coverage rates or application conditions.

Always follow the manufacturer's application and safety instructions, and test a small area if you are unsure about coverage.

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